The present invention relates generally to vehicle brake shoe assemblies, and in particular, to a high friction drum-in-hat brake shoe assembly incorporating a plurality of carrier plate extensions through a friction material matrix, to be utilized in vehicle parking brakes and vehicle emergency braking systems on vehicle equipped with four wheel disc brakes.
Vehicle drum type friction brakes commonly include a vehicle brake shoe assembly carrying a frictional matrix which is brought into contact with an inner cylindrical surface of a rotating brake drum to generate a frictional force and correspondingly slow, stop, or hold the vehicle in a stationary or parked position.
Variations between the curvature of the brake shoe assembly and the curvature of the inner cylindrical surface of the rotating brake drum can alter the frictional effectiveness of a drum type friction brake. For example, if the friction level generated by a drum type friction brake is too low due to regions of the frictional matrix which are not in contact with the opposing friction surface of the brake drum, the brake will not function to the required level of static effectiveness, i.e. parking brake capability. One method commonly utilized to overcome this type of static friction problem is to bring the vehicle to a stop a number of times using only the parking brake or emergency brake, thereby generating excessive frictional forces on those portions of the brake shoe assembly in contact with the rotating brake drum, and wearing or abrading them into closer conformance with the curvature of the rotating brake drum. Such methods can cause premature failure or excessive wear on the brake components.
Alternatively, frictional braking forces are increased in vehicle drum type friction brakes by producing a rough or sandblasted friction surface on the brake drum which is engaged by the brake shoe assembly. This process, while increasing the frictional braking forces may, reduced the amount of friction material, shortening the lifespan of the brake components such as the brake friction material matrix.
The use of carrier plate extensions, nubs or teeth, which are completely contained within, and engage with, the brake friction material matrix on brake shoe assemblies has been previously employed to facilitate the attachment and interlocking of the brake friction material matrix to the carrier plate. See, for example, U.S. Pat. No. 6,367,600 B1 to Arbesman and U.S. Pat. No. 6,279,222 B1.
Another example of the use of projecting nubs or teeth is seen in U.S. Pat. No. 4,569,424 to Taylor, Jr., where an improved brake shoe assembly is provided. A friction material matrix in the '424 Taylor, Jr. reference is molded directly onto a brake liner plate which includes a plurality of perforations forming protruding tabs. The inter-engagement between the molded friction material and the perforated areas and tabs provides an enhanced interlocking strength between these elements. The '424 Taylor, Jr. reference, specifically teaches that it is undesirable for the protruding tabs to extend so far as to reach the outer surface of the friction material matrix, and indicate that the brake shoe assembly has reached the end of a useful service life when sufficient friction matrix material has been worn away so as to expose the protruding tabs.
Accordingly, there is a need in the automotive brake systems design area for a parking brake or emergency brake shoe assembly with enhanced static and dynamic frictional properties, and which does not require an initial wear or break-in period to improve conformance between the frictional matrix and the opposing frictional surface of the brake drum.